1. Field of the Invention
The present invention is directed to a method for controlling a dynamic scale and to a corresponding arrangement therefor, for use in a dynamic scale which weighs a piece of mail during a conveying event, particularly for a fast processing of mixed mail in a scale and franking system. The inventive method is suitable for users of mail-processing systems with a dynamic scale and postage-calculating postage meter machine as well as with dynamic postage calculating scales and franking devices.
2. Description of the Prior Art
xe2x80x9cMixed mailxe2x80x9d means an unsorted stack of pieces of mail. The term xe2x80x9clettersxe2x80x9d is used below as a representative term for all other possible pieces of mail as well.
Dynamic letter scales are known. For example, Francotyp-Postalia AG and Co. distributes a dynamic letter scale as component of an automatic mail system Francopost 12.000. The letters are introduced as a stack and are first automatically separated. The separated letters are accepted by the dynamic weighing unit and their weight is identified. The weight determination must ensue with a precision that enables the allocation of the letters to the correct postage class. The postage is automatically transmitted to the connected franking unit, is billed and printed onto the letter. Upon placement of the letter onto the weighing pan and the transport thereof, mechanical vibrations are transmitted to the weighing cell, the amplitude thereof being approximately proportional to the absolute letter weight. These noise vibrations limit the precision of the measuring result. In general, a measuring precision of 1 g is specified in dynamic letter scales up to a letter weight of 1000 g. Letters that are heavier cannot be precisely weighed with this device, in manner which would enable an automatic postage setting of the franking unit. Such letters then must be separately weighed with a suitable, static scale. The corresponding postage must then be manually entered into the franking unit. The automatic execution is thus interrupted. Especially disadvantageous is the fact that the mail shipper cannot predict whether a specific letter that is introduced in common with the others as a stack will or will not exceed this weight limit.
U.S. Pat. No. 4,778,018 discloses a dynamic letter scale wherein the weighing pan is resiliently suspended relative to the conveying mechanism. The transmission of vibrations from the conveying mechanism to the weighing cell are intended to be attenuated by this arrangement. This damping, however, is adequate given high weights in order to assure an adequate measuring precision. Moreover, a resilient suspension produces an intrinsic oscillation of the weighing pan that lengthens the measuring time and thus reduces the letter throughput.
U.S. Pat. No. 5,014,797 discloses a non-modular apparatus for automatic mail processing wherein the dynamic weighing function is integrated in the franking unit. A shortening of the conveying paths and a letter throughput per time unit that is higher overall are thus achieved. Again, however, the maximum weight is limited given a prescribed measuring precision and processing speed. A product constructed according to this solution achieves a throughput of approximately 5,000 letters per hour given a maximum weight of 500 g. For pieces of mail having a higher weight, the manufacturer offers an additional static scale, thus an automatic processing of pieces of mail that one higher in weight is not possible.
U.S. Pat. No. 4,956,782 and British Specification 22 35 656 disclose semi-dynamic weighing. A user station arranged upstream in the processing chain can be a scale and a user station arranged downstream is a postage meter machine. A continuously moving piece of mail must be completely accepted by the scale for the measuring time required for weight identification. Given mixed mail, the probability is higher that the scale could determine an incorrect measured result. The measuring time is lengthened dependent on the dimensions of the letter. A complicated control that interprets the dimensions of the letter in advance and controllable motors are required for this purpose. Alternatively, the weighing path could be lengthened and a reject compartment could be provided, however, this would increase the length of the overall mail-processing system, which is not possible without more extensive retrofitting.
According to European Application 514 107, a control means interrupts transport given pieces of mail that are large and difficult to weigh until the measurement is stable. A detector is arranged in the scale close to the end of the conveyor belt at a downstream location, this detector only allowing a letter to pass whose weight has been identified before this point in time. Measuring errors occur given a short weighing path and unequally distributed mass in the letter or given a high conveying speed of high-mass letters. Given a stop, moreover, the letter can slide off the weighing pan due to its inertia. The dimensions of the weighing pan are therefore designed somewhat larger, or the conveying speed is fixed lower. The throughput given mixed mail is correspondingly reduced.
German Published Application 37 31 494 (U.S. Pat. No. 4,753,432) discloses that a resting time be provided in the weighing procedure, during which operation of the franking system and the transport system is interrupted because continued operation would otherwise produce too large a vibration. The transport time from the weighing module to the postage meter machine is selected short, however, the speed cannot be arbitrarily increased without increasing the risk of a jam of letters. The item output that can be achieved is limited by the pauses inserted into the executive sequence. The speed of weighing is limited by the speed of the weight identification, which causes a greater outlay given heavy pieces of mail when the measurement must be exact.
With the goal of increasing the throughput of pieces of mail per hour, an object of the invention is to achieve an automatic processing of pieces of mail even having higher weight, without a need for manual interventions during the mail processing. Alternative weighing means should be eliminated. An optimally high proportion of the outgoing mail of the mail shipper should be weighed in the dynamic mode.
The above object is achieved is achieved in accordance with the principles of the present invention in a method and an apparatus for controlling a dynamic scale which processes mixed mail, consisting of items having different weights, for use with a further processing station connected downstream from the dynamic scale, wherein the dynamic scale is set according to particular requirements for processing a mixed mail stack, this setting taking place through an input unit and ensuing on the basis of selected shipping parameters and/or operating parameters, and wherein operating parameters and data for the scale are modified according to the setting with the modified parameters and data being stored in a non-volatile memory, and wherein a supplied postal item from the stack of mixed mail is conveyed through the dynamic by a conveyor arrangement and is weighed therein and is transported from the dynamic scale to the further processing station dependent on the operating parameters and data which have been set.
The scale is basically composed of conveyor arrangement, weighing pan, a weighing cell as well as an electronic control and evaluation unit. The weighing pan preferably has a rectangular shape, with its dimension oriented transversely relative to the conveying direction minimally corresponding to the maximum letter format plus a tolerance allowing for admission of the letter to the weighing pan. The dimensioning of the weighing platform in the conveying direction must correspond to the maximum longitudinal format of the postal matter plus a distance that is traversed by the item being weighed during the weighing procedure. It is of no significance for the realization of the invention whether the pieces of mail are transported vertically or horizontally. A known weighing method can be employed in the weighing cell.
The inventive scale can, for example, be operated in three operating modes that are respectively adapted to the differing composition of the stack of letters to be processed:
1. The stack contains letter that all have the same weight, for example an advertising mailing with identical content. A weighing of the individual letters is thus omitted. In the first operating mode, the control unit outputs a control instruction for the maximum conveying speed to the drive of the conveying mechanism of the scale.
2. The stack contains mainly letters having the same weight, for example an advertising mailing with mainly identical enclosures, but also, a few letters to addressees which contain more extensive enclosures. In this case, it is beneficial to merely monitor a weight threshold, which is not exceeded by the great majority of letters having a known weight (upper threshold). The converse case of monitoring a lower threshold, which is exceeded by the great majority of letters is likewise possible. These thresholds can be set by the user via the input and output unit. Merely making a selection of the type of shipping suffices for frequently occurring shipping types having fixed threshold, for example infomail, as a result of which an appropriate, stored threshold is automatically activated (for example, infomail standard equals 20 g). Letters that lie beyond the threshold can, for example, be separated out of the letter stream. In general, the measuring precision and/or the conveying speed can be adapted to the height of the respective threshold by threshold monitoring. A low, upper threshold (for example 100 g) allows a relatively high conveying speed because weights below this threshold require only a very short time on the weighing platform, and higher weights need not be exactly measured since the fact that they are higher than the threshold already suffices.
3. The stack contains letters differing in weight (mixed mail). Each letter must be identified in terms of its weight with adequate precision and the postage must be calculated on the basis of this measured value. For example, an adequate precision and optimum conveying speed can be achieved when an upper measuring limit is set below which the individual letter weights lie.
The term xe2x80x9cadequate precisionxe2x80x9d expresses the relationship between absolute measuring precision (no tolerance), upper limit of the measuring range and measuring time. The measuring time is limited by the path that the letter traverses on the weighing pan given a predetermined conveying speed. It can only be increased by lengthening the weighing pan or by reducing the conveying speed. Given a predetermined (fixed dimension) scale, only the latter of the two possibilities comes into consideration. A high measuring precision is obtainable only at the expense of the other two parameters of upper limits of the measuring range and the conveying speed, and therefore should be selected only as high as necessary in the interest of the customer. Typically a customer does not want to undergo a complicated xe2x80x9cpostage duexe2x80x9d payment procedure due to a weight that was identified too low, but wants to avoid an excessively high postage not being paid due to a weight that was measured too high. The balancing of these demands is dependent on the structure of the postage rates. If, for example, the postage rates of a mail shipping company change in respective steps of 20 g, then relatively high measuring precision is required over the entire range of measurement. When the customer ships mainly xe2x80x9cnormalxe2x80x9d letters most likely having low weight under these conditions, then a setting of the dynamic scale is possible that combines a high measuring precision of, for example, 0.5 g given average processing speed with a low, upper measuring range limit of, for example, 400 g for the dynamic mode. In another instance, the postage structure may be only slightly differentiated (stepped) in view of the weight. For example, there is the same upper weight limit of 1000 g at the Deutsche Post AG (DPAG) for shipping xe2x80x9cinfomail-largexe2x80x9d and xe2x80x9cinfomail-maxixe2x80x9d below which the postage is independent of the weight. In this case, an optimum setting of the dynamic scale would ensue such that it would only monitor this limit value (see operating mode 2). Since an absolute precision of 10 g is adequate here, a relatively high conveying speed can still be enabled during weighing.
Dependent on the requirements for processing a particular stack of mixed mail, the inventive method allows an optimum setting of the dynamic scale, the setting optionally ensuing on the basis of selected shipping parameters and/or operating parameters. The setting of the dynamic scale ensues with three weighing parameters (measuring range, precision, speed) that are dependent on one another in terms of their magnitude, so that the modification of one parameter leads to the modification of at least one of the other parameters. Any modification of the control of the scale is monitored and is displayed via a display unit.